Optical comparator circuit

ABSTRACT

An optical connector assembly (1) for connecting an optical fiber (9), an optical element (4) (light-emitting element or light-receiving element), and an electric circuit together. A bolt (32) of an optical fiber-mounting fitting in which the optical fiber (9) is inserted in the hole of an electic seal (32) and a bolt (31), is screwed into a threaded hole formed in a housing (2) of the plug (1) that accommodates the optical element (4) in order to couple the optical fiber (9) to the plug (1). The connection between the optical element (4) and the electric circuit is accomplished by a jack (20) and the plug (1) is provided with a lock mechanism based on a push-type lever (20), featuring improved sealing performance against water, oil, dust and dirt.

This application is a division of U.S. Ser. No. 499,549, filed Jun. 27,1990, now U.S. Pat. No. 5,163,109, issued Nov. 10, 1992.

TECHNICAL FIELD

The present invention relates to an optical connector assemblyemployable for a signal sending apparatus wherein electrical signals areconverted into optical signals and the converted optical signals arethen sent via an optical fiber or a signal receiving apparatus whereinoptical signals received via an optical fiber is converted intoelectrical signals and the converted electrical signals are then takenout of the signal receiving apparatus.

BACKGROUND ART

An optical connector assembly is an essential device required forconstituting an optical communication system, an optical measuringsystem or the like system wherein various instruments, apparatuses,equipments or optical circuit components are connected to each other viaoptical fibers. A main function of the optical connector assembly is toconnect an optical fiber to an optical element (in the form of a lightemitting element or a light receiving element) and moreover connect theoptical fiber to an electrical circuit or electrical circuits.

FIGS. 1 and 2 typically show a conventional optical connector assemblyby way of a perspective view, respectively.

The optical connector assembly as shown in FIG. 1 comprises an opticalconnector X₁ having end parts A₁ and A₂ of a two-core type optical fiberA protruded therefrom to firmly hold the optical fiber A and aphotoelectric converting module X₂ including a photoelectric convertingelement. With this conventional optical connector assembly, connectingof the optical connector X₁ to the photoelectric converting module X₂ iscarried out by fitting the optical connector X₁ to the photoelectricconverting module X₂ and then actuating a locking mechanism P₂. Inaddition, electrical/mechanical connection of the photoelectricconverting module X₂ to a printed-circuit board G is carried out byusing a lead frame P₁ which is arranged below the photoelectricconverting module X₂.

On the other hand, the conventional optical connector assembly as shownin FIG. 2 includes an integrated type optical module X₃ in which aphotoelectric converting element is received s that the foremost end ofan optical fiber A comes in contact with a light emitting surface or alight receiving surface of the photoelectric converting element. Anelectric plug P₂ is attached to the end surface of the optical module X₃so that the optical module X₃ is coupled to an electrical module X₄ byfitting the electrical plug P₂ into an electrical jack (not shown).Connection of the electrical module X₄ to a printed-circuit board G iscarried out by using a lead frame P₁ in the same manner as describedabove with reference to FIG. 1.

In this manner, connecting/disconnecting of the conventional opticalconnector assembly is accomplished by a simple fitting operation for theaforementioned respective components.

Thus, the conventional optical connector assembly can be used withoutany particular problem for an apparatus or an equipment installed in acalm and dustless environment, e.g., an audio apparatus, an apparatusfor hospital, office or the like facilities. However, when theconventional optical connector assembly is used for an apparatus or anequipment operable in a severe environment including vibration, noisysound, various contaminated material, moisture or dust, e.g., facilitiesin a factory, an industrial machine or the like, there arise problemsthat electrical noise is generated due to vibration, noisy sound or thelike, a connector falls down naturally, and a running life of aconnector and associated components is shortened due to the presence ofoily contaminated material, dust or the like foreign material.

In addition, since no seal is employed for connecting/disconnectinglocations in components constituting the conventional optical connectorassembly, there arises another problem that no optical communication canbe made because oil, dust or the like foreign material enters theinterior of the optical connector assembly via connecting/disconnectinglocations. For the reason, requirements have been raised for developingan optical link which can be used in field under a severe environmentalcondition due to invasion of water, oil, dust or the like foreignmaterial, even when optical communication is used between controllersfor machines (robots, machine tools, presses etc.) installed for factoryautomation.

Hitherto, the conventional optical connector assembly is commerciallysold in a stationary state wherein an optical fiber A is immovably heldin a module X₁ or X₃ as in the case of the optical connector X₁ shown inFIG. 1 or the integrated type optical module X₃ as shown in FIG. 2.Thus, there arises another problem that it is difficult to adequatelyadjust a length of the optical fiber A in field by a cutting operationor a connecting operation, because connection or disconnection of theoptical fiber A in field is substantially impossible.

When an optical fiber is fitted into an optical connector, hitherto, theoptical fiber A is first cut to a predetermined length by actuating aplier, a nipper or the like tool. Thereafter, to make the rugged endsurface of the optical fiber A flat correctly, a sheath is removed fromthe optical fiber by a distance of 1 to 2 mm as measured from the endsurface of the optical fiber A and then the end surface of a core A_(a)of the optical fiber A is brought in contact with a hot plate 101 or anabrasive paper (not shown), as shown in FIG. 3. After heating orgrinding the end surface of the core A_(a), a rubber seal is fittedround the core A_(a) at a suitable position away from the end surface ofthe core A_(a).

However, if the optical fiber A is excessively heated or ground, thereis a danger that the sheath may be deformed, as shown in FIG. 4,resulting in the optical fiber A being undesirably damaged or injured.In such a case as described above, it becomes impossible to insert theoptical fiber into a hole on the optical connector. Even though theoptical fiber could be inserted into the hole, an optical couplingefficiency of the optical fiber and other optical factors may bedegraded.

In a case where the conventional optical connector assembly is used asan optical signal sending module for optical communication, lightgenerated by a light emitting diode (hereinafter referred to as a LED)is transmitted via an optical fiber but the light is dampened more andmore as a length of the optical fiber, i.e., a distance, of transmissionof optical signals is elongated.

To assure that a constant quantity of light is always receivedregardless of how far a distance of signal transmission is elongated, acircuit structure as shown in FIG. 5 has been heretofore employed.

Referring to FIG. 5, an optical signal sending module 102 includes a LED103 and a switching transistor 104 as essential component for thepurpose of optical communication. In response to inputting of signaldata SIG via a terminal T₂, the transistor 104 is turned on or off andthereby the LED 103 is turned on or off. The module 102 is connected toa power supply source circuit 105 via a terminal T₁. The circuit 105includes a direct current power supply source 106 and a plurality offixed resistors R₁, R₂, - - - R_(n) connected to the power supply source106 in parallel therewith. One of a plurality of terminals S₁, S₂, - - -S_(n) on the circuit 105 side is connected to the terminal T₁ on theoptical module 102 side so that an intensity of light generated by theLED 103 is correctly adjusted by feeding an adequate intensity ofelectric current to the LED 103 corresponding to the present distance ofsignal transmission.

A structure wherein a variable resistor 107 is connected to the LED 103in the optical module 102 in series as shown in FIG. 6 is known as otherexample of the foregoing kind of prior art. Additionally, arrangement ofan adjustable resistor 108 outside of the optical module 102 as shown inFIG. 7 is known as another example of the prior art. With theconventional structure as shown in FIGS. 6 and 7, however, it isnecessary that a suitable resistor on the circuit 105 side is selectedfrom among the plural resistors for the optical module 102 and the thusselected resistor is connected to the optical module 102 at a positionoutside of the optical module 102. Particularly, with the conventionalstructure as shown in FIG. 6, it is necessary that the variable resistor108 is adjusted correctly. For the reason, there arises a problem thathandling of the optical fiber in field and a setting operation for alength of the optical fiber in field become complicated.

In a case where the aforementioned conventional optical connectorassembly is used as a signal receiving module for optical communication,in response to receiving of an optical signal, an output from theoptical connector assembly is delivered to a printed-circuit boardelectrically connected to the optical connector assembly, whereby thesignal in the form of an output from the optical connector assembly isprocessed in a signal processing circuit mounted on the printed-circuitboard. However, it is essential, from viewpoint of a necessity fordemodulating the optical signal thereby to check the content of dataincluded in the optical signal, that an optical signal receiving circuitfor converting the optical signal into an electrical signal thereby todiscriminate the content of a logical level of the electrical signal isarranged in each signal receiving section in the optical communicationsystem.

In fact, the applicant of the present invention invented an opticalsignal receiving circuit employable for an optical communication systemwherein the content of a logical level of an input signal can bediscriminated without any adverse effect of the input signal on anoffset voltage and moreover a duty ratio of the discriminated outputsignal can be maintained normally and he filed an application for patentlater (refer to Japanese Patent Application NO. 175694/1987).

This prior invention discloses a comparator circuit as shown in FIG. 8which is constructed in a two-stage structure comprising a firstcomparator 110 and a second comparator 120 situated at the later stage.The conventional comparator circuit is constructed such that the contentof a logical level of a received signal (input signal) is discriminatedindependently of an offset voltage of the received signal by makingcomparison in the first comparator 110 as to a level of the receivedsignal and incorrect variation of a duty ratio of the discriminatedsignal is automatically corrected by making comparison in the secondcomparator 120 as to a level of the discriminated signal to reverse amanner of inputting a signal corresponding to the input signal and avoltage (signal) corresponding to the threshold voltage relative to thefirst comparator 110.

With the above construction, the comparator circuit can accomplish theinitially intended object without fail. As shown in FIG. 8, however, thefirst comparator 110 and the second comparator 120 are activated with aconstant magnitude of voltage V_(cc) derived from the power supplysource.

Specifically, when a transistor 111 in the first comparator 110 at thefirst stage fails to be activated because a voltage appearing at acollector of the transistor 111 is held at a level of V_(cc), i.e., whenan output derived from the comparison made in the first comparator 110is held at a logical "1" level, a value of voltage indicative of theoutput derived from the comparison is raised up near to the voltageV_(cc) appearing at the collector of the transistor 111.

On the other hand, the second comparator 120 is likewise activated withthe voltage V_(cc) derived from the power supply source.

In this case, an input voltage required for normally operating thesecond comparator 120 is set to a voltage value substantially equal toabout 80% of the voltage V_(cc) of the power supply source depending oncharacteristics of the second comparator 120.

Therefore, when an output (a signal remaining at a logical "1" level)derived from the comparison in the first comparator 110, the outputbeing boosted near to the voltage V_(cc) of the power supply source, isinputted into an input terminal of the second comparator 120, therearises a problem that the second comparator 120 may incorrectly beoperated, resulting in an exact output failing to be obtained.

FIG. 9(c) shows a time chart which illustrates a desirable output waveform of the comparator 120. Once the second comparator 120 isincorrectly operated, phase deviation occurs, as shown in FIG. 9(a).Otherwise, a signal may be deformed at the time of signal rising, asshown in FIG. 9(b).

DISCLOSURE OF THE INVENTION

The present invention has been made with the foregoing problems in mind.

An object of the present invention is to provide an optical connectorassembly which can be used for apparatuses and equipments operable in asevere environment including vibration, noisy sound, variouscontaminated material, moisture or dust.

Other object of the present invention is to provide a jig for treatingthe foremost end surface of an optical fiber wherein the jig can preventa sheath of the optical fiber from being deformed due to heat orfriction when the foremost end surface of the optical fiber is heated orground.

Another object of the present invention is to provide an apparatus forsending optical signals wherein an adequate intensity of power derivedfrom light generated by a light emitting diod can easily and quickly betransmitted in field by a distance of transmission differing independence on a length of the optical fiber without any particularnecessity for adjusting variable resistors or arranging resistorsoutside of the apparatus.

Further another object of the present invention is to provide acomparator circuit including comparators in two-stage structure whereinthe circuit can reliably prevent a comparator situated at a later stagefrom being operated incorrectly.

To accomplish the above objects, there is provided according to oneaspect of the present invention an optical connector assembly comprisingan optical fiber fitting unit including an elastic seal and a bolt, theelastic seal being formed with a hole at the central part thereof andthe bolt being likewise formed with a hole at the central part thereofso that an optical fiber extends through the hole of the elastic sealand the hole of the bolt; a jack including a plurality of contacts, ahousing of the jack being formed with a plurality of elastic levers inthe form of push levers; and a plug including a light emitting elementor a light receiving element and a plurality of contacts electricallyconnected to the light emitting element or the light receiving elementand adapted to come in contact with the plural contacts of the jack, ahousing of the plug being formed with a threaded hole opposite to alight emitting surface of the light emitting element or a lightreceiving surface of the light receiving element as well as a pluralityof apertures of which contour is designed to coincide with a contour ofeach of the elastic levers so as to allow each elastic lever to bedetachably fitted into the corresponding aperture; whereby the opticalfiber is coupled to the plug by threadably fitting a plurality of malethreads on the bolt of the optical fiber fitting unit into the threadedhole of the plug.

With such construction, the optical fiber fitting unit is connected tothe plug via threadable fitting. An elastic seal is interposed betweenthe plug and the jack, and plug is coupled to the jack with the aid of alocking mechanism comprising a plurality of apertures and a plurality ofelastic levers in the form of push levers each adapted to be fitted intothe corresponding aperture. Thus, an industrial apparatus or equipmentcan be operated even in a severe environment including vibration, noisysound, various contaminated material or dust without an occurrence ofmalfunctions that electrical noise is generated, a connector falls downnaturally and a running life of components constituting the connector isshortened. Since the optical fiber fitting unit is threadably connectedto the plug, a length of the optical fiber can be adjusted easily. Inaddition, positional displacement, maintenance service or repairingoperation for various apparatuses each utilizing optical communicationcan be carried out at a high efficiency.

Further, according to the present invention, an O-ring is interposedbetween the plug and the jack and moreover a packing is interposedbetween the jack and the wall surface of a casing to which the jack isattached. Consequently, sealability of the optical connector assemblyagainst oil, dust or the like foreign material can be improved further.

According to other aspect of the present invention, there is provided anoptical connector assembly comprising an optical fiber fitting unitincluding an elastic seal and a cover of which sectional shape isdesigned in an E-shaped contour, the elastic seal being formed with ahole at the central part thereof and the cover being formed with a holeat the central part as well as a plurality of female threads on theinner wall thereof so that an optical fiber extends through the hole ofthe elastic seal and the hole of the cover; an optical module includinga cylindrical housing which is formed with a through hole extendingalong a center axis of the housing, a light emitting element or a lightreceiving element being received in the hole such that a light emittingsurface of the light emitting element or a light receiving surface ofthe light receiving element intersects the center axis of thecylindrical housing at a right angle, a plurality of male threads beingformed round the outer periphery at one end part of the cylindricalhousing and a plurality of female threads being formed round the innerperiphery at the other end part of the cylindrical housing; and anelectrical module including a plurality of contacts which are connectedto the light emitting element or the light receiving element via aplurality of electrical wirings, the electrical module being formed witha plurality of male threads round the outer periphery of a cylindricalhousing thereof, the male threads being threadably engaged with thefemale threads round the inner wall of the cylindrical housing for theoptical module; whereby the optical fiber is coupled to the opticalmodule by threadably fitting the female threads of the cover for theoptical fiber fitting unit onto the male threads of the cylindricalhousing for the optical module, while the elastic seal is tightlyencased in the hole of the optical module.

With such construction, since the optical module, the optical fiberfitting unit, the optical module and the electrical module are connectedto each other via threadable fitting, sealability of the opticalconnector assembly against water, oil, dust or the like foreign materialcan be improved further and the optical connector assembly can normallybe used even in an undesirable environment.

Alternatively, the elastic seal in the optical fiber fitting unit may beeliminated. In this case, at least a projection in the cover extendingalong a center axis of the optical connector assembly is made of elasticmaterial.

According to another aspect of the present invention, there is provideda jig for treating the foremost end surface of an optical fibercomprising an optical fiber fitting unit including an elastic seal and abolt, the elastic seal being formed with a hole at the central partthereof and the bolt being formed with a hole at the central partthereof so that an optical fiber extends through the hole of the elasticseal and the hole of the bolt, a first jig of which one end part ismachined in the form of a threaded hole adapted to threadably receivethe bolt and of which other end part is machined in the form of a guidehole which is communicated with the threaded hole, the guide hole beingdimensioned to have an inner diameter substantially equal to an outerdiameter of the optical fiber; and a second jig having a hole formed atthe central part thereof, the hole being dimensioned to have an innerdiameter substantially equal to an outer diameter of the optical fiber;whereby the bolt of the optical fiber fitting unit is threadably fittedinto the threaded hole of the first jig, while the first jig is held inclose contact with the second jig, and thereafter the second jig isdisconnected from the first jig so as to allow the foremost end surfaceof the optical fiber to be treated.

With such construction, a distance between the foremost end surface ofthe optical fiber extending through the guide hole and the end surfaceof the first jig is kept constant. Since a sheath of the optical fiberis firmly retained in the guide hole, an occurrence of deformation dueto heat or friction caused by a grinding operation for a core of theoptical fiber can be prevented reliably.

According to another aspect of the present invention, there is providedan apparatus for sending optical signals wherein a switching circuit isturned on or off depending on data to be sent and a light emitting diodefor optical communication electrically connected to the switchingcircuit is turned on or off in response to ON or OFF of the switchingcircuit so that light generated by the light emitting diod which hasbeen turned on or off is sent as a signal for optical communication viaan optical fiber, the apparatus comprising a plurality of fixedresistors electrically connected to the light emitting diode for opticalcommunication in parallel therewith, and a plurality of terminalselectrically connected to one ends of the fixed resistors so that apredetermined magnitude of voltage is applied to the terminals from apower supply source, wherein the light emitting diode for opticalcommunication, the switching circuit and the fixed resistors areintegrated in a single module.

With such construction, since the optical signal sending apparatusincludes a plurality of fixed resistors for previously adjusting anintensity of power of emitted light in dependence on a distance of theoptical fiber in a light emitting diode driving circuit based on a powerof light generated by the light emitting diode and a dampening valuerelated to the distance of the optical fiber and further includes aplurality of terminals connected to the fixed resistors in series so asto allow a voltage of the power supply source to be applied to theterminals, the apparatus can easily and quickly be adjustedcorresponding to a distance of transmission of optical signals merely byconnecting the power supply source to the corresponding connector pins,even in a case where a length of the optical fiber is to be adjusted infield.

According to another aspect of the present invention, there is providedan apparatus for sending optical signals wherein a switching circuit isturned on or off depending on data to be sent and a light emitting diodefor optical communication electrically connected to the switchingcircuit is turned on or off in response to ON or OFF of the switchingcircuit so that light generated by the light emitting diode which hasbeen turned on or off is sent as a signal for optical communication viaan optical fiber, the apparatus comprising a plurality of fixedresistors electrically connected to the light emitting diode for opticalcommunication in series, and a plurality of terminals electricallyconnected to each other in series so that a predetermined magnitude ofvoltage is applied to the terminals from a power supply source, whereinthe light emitting diode for optical communication, the switchingcircuit and the fixed resistors are integrated in a single module.

According to this embodiment of the present invention, since the pluralfixed resistors included in the apparatus are electrically connected tothe light emitting diode in series, there is no danger that an electriccurrent of which intensity exceeds the maximum rated value is fed to thelight emitting diode, even in a case where two or more terminals areincorrectly connected to the power supply source. Consequently, theapparatus can reliably prevent the light emitting diode from beingundesirably damaged or injured.

According to another aspect to the present invention, there is provideda comparator circuit including a first comparator at a first stage and asecond comparator at the second stage, wherein a voltage derived fromdividing of the voltage of the power supply source is applied to anoutput terminal of the first comparator and a voltage to be inputtedinto an input terminal of the second comparator is restricted to assumea voltage value within a predetermined range set for allowing the secondcomparator to be normally operated.

According to further another aspect of the present invention, there isprovided a comparator circuit including a first comparator at a firststage and a second comparator at a second stage, wherein a voltage ofthe power supply source to be applied to the second comparator isboosted so that an input voltage outputted from the first comparatorraises up the upper limit voltage value for the second comparator withina predetermined range for allowing the second comparator to be normallyoperated.

With such construction, since it is assured that the comparator at thelater stage in the comparator circuit constructed in a two-stagestructure is normally operated at all times, an exact output wave formcan be obtained reliably. Consequently, when the comparator circuit asconstructed in a two-stage structure in that way is employed for anoptical signal receiving circuit or the like circuit for opticalcommunication, reliability of data derived from demodulating of opticalsignals can be improved substantially.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 9 are a view illustrating a prior art, respectively,

FIG. 10 is a sectional view of an optical connector assembly inaccordance with an embodiment of the present invention,

FIG. 11 is a sectional view illustrating a plug for the opticalconnector assembly in accordance with the embodiment of the presentinvention shown in FIG. 10,

FIG. 12 is a perspective view illustrating an optical fiber fitting unitfor the optical connector assembly in accordance with the embodiment ofthe present invention shown in FIG. 10,

FIG. 13 is a plan view illustrating the plug in FIG. 11,

FIG. 14 is a side view illustrating the plug in FIG. 11,

FIG. 15 is a plan view illustrating a jack for the optical connectorassembly in accordance with the embodiment of the present invention inFIG. 10,

FIG. 16 is a side view of the jack in FIG. 15,

FIG. 17 is a sectional view of an optical connector assembly inaccordance with other embodiment of the present invention,

FIG. 18 is a sectional view illustrating by way of example a jig fortreating the foremost end surface of an optical fiber,

FIG. 19 is a perspective view illustrating the jig in FIG. 18 in adisassembled state,

FIG. 20 is a sectional view illustrating an undesirable case where theprior art is applied to an optical connector assembly,

FIG. 21 is a sectional view illustrating an optical connector assemblyin accordance with another embodiment of the present invention,

FIG. 22 is a sectional view of an optical module for the opticalconnector assembly in accordance with the embodiment of the presentinvention shown in FIG. 21,

FIG. 23 is a perspective view illustrating an optical fiber fitting unitfor the optical connector assembly in accordance with the embodiment ofthe present invention shown in FIG. 21,

FIG. 24 is a sectional view illustrating an optical connector assemblyin accordance with further another embodiment of the present invention,

FIG. 25 is a schematic perspective view illustrating an optical signalsending module of the optical connector assembly in accordance with thepresent invention,

FIG. 26 is a circuit diagram employable for the optical signal sendingmodule in FIG. 25,

FIG. 27 is a circuit diagram employable for the optical signal sendingmodule in accordance with a modified embodiment of the presentinvention,

FIG. 28 is a circuit diagram illustrating by way of example a circuitemployable for a comparator required for using the optical connectorassembly of the present invention, and

FIGS. 29 to 32 are a circuit diagram illustrating a circuit employablefor a comparator in accordance with a modified embodiment of the presentinvention, respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be described in detail hereinafter withreference to the accompanying drawings which illustrate preferredembodiments thereof.

FIGS. 10 to 16 show an optical connector assembly in accordance with afirst embodiment of the present invention, respectively. FIG. 10 is asectional view which illustrates the whole structure of the opticalconnector assembly of the present invention, FIG. 11 is a sectional viewwhich illustrates structure of a plug 1 side (i.e., female connectorside) before an optical fiber 9 is fitted to the plug 1, FIG. 12 is aperspective view which illustrates an optical fiber 30 side before theoptical fiber 9 is fitted to the plug 1, FIG. 13 is a plan view of theplug 1, FIG. 14 is a side view of the plug 1 as seen in an arrowA-marked direction (see FIG. 10), FIG. 15 is a plan view of a jack 20,and FIG. 16 is a side view of the jack 20 as seen in an arrow B-markeddirection (see FIG. 10). Basically, the optical connector assemblyincludes a plug 1 and an optical fiber fitting unit 30 (see FIG. 12) asessential components. The optical connector assembly of the presentinvention is constituted by connecting these components to each other insuch a manner as described later.

Referring to FIG. 11, a hollow space 3 is formed at the central part ofa housing 2 for the plug 1 and a light emitting element or a lightreceiving element 4 is received in the hollow space 3. When the opticalconnector assembly of the present invention is used as a signal sendingmodule, the light emitting element 4 is received in the hollow space 3.To the contrary, when the optical connector assembly is used as a signalreceiving module, the light receiving element 4 is likewise received inthe hollow space 3. The light emitting element and the light receivingelement are hereinafter generally referred as an optical element.

Specifically, a contact member 6 having six female contacts 5 formedthereon (see FIG. 14) is fastened to the housing 2 of the plug 1 by aplurality of bolts 14 (or by using an adhesive), and a card edge wiringboard 7 is firmly supported by the side wall of the contact member 6 incooperation with the side wall of the housing 2. Electrical connectionof the card edge wiring board 7 to the contact member 6 is accomplishedby card edge connectors 8 which are bridged between the side wall of thecontact member 6 and the card edge wiring board 7. The optical element 4is mounted on the card edge wiring board 7 so that light coming from anoptical fiber 9 is converted into an electrical signal by the opticalelement 4 or light derived from conversion from an electrical signalinto an optical signal is transmitted to the optical fiber 9. Theoptical element 4 is surrounded by an adaptor 11 which is formed with aguide hole 10 through which the optical fiber 9 is inserted. An innerdiameter of the guide hole 10 is dimensioned to coincide with an outerdiameter of the optical fiber 9. It should be noted that the guide hole10 is located opposite to a light emitting surface or a light receivingsurface of the optical element 4.

The housing 2 of the plug 1 has a projection 12 which is located abovethe hollow space 3, and the projection 12 is also formed with a guidehole 13 in alignment with the guide hole 10 in the adaptor 11. Inaddition, a threaded hole 16 including a number of female threads 15 isformed in a region above the guide hole 13 in alignment with the latter.

As shown in FIG. 12, the optical fiber fitting unit 30 comprises a bolt31 and an elastic seal 32. A hole for allowing the optical fiber 9 toextend therethrough is formed in the bolt 31 along a center line of theoptical fiber fitting unit 30. Similarly, a hole for allowing theoptical fiber 9 to extend therethrough is likewise formed in the elasticseal 32 along the center line of the optical fiber fitting unit 30.Therefore, the optical fiber 9 extends through the hole in the bolt 31and the hole in the elastic seal 32.

As is apparent from FIG. 10, when the bolt 31 is threadably engaged withthe threaded hole 16, the foremost end of the optical fiber 9 is broughtin close contact with the light emitting/receiving surface of theoptical element 4, while the elastic seal 32 is tightly encased in aspace below the threaded hole 16. In the case as shown in FIG. 10,sealability is enhanced by tightly placing a seal cap 33 on the bolt 31.

Apertures 17 and 18 are formed on the housing 2 of the plug 1 at twolocations on the jack 2 side and rectangular projections 19 areprojected on the inner wall of the housing 2 at two locations on thejack 20 side.

On the other hand, a housing 21 of the jack 20 is fastened to the sidewall 23 of a box-shaped casing for a wiring panel or the like componentsby tightening four bolts 22, and six male contacts 24 are projected inthe interior of a hollow space in the housing 21. Thus, electricalconnection is established between the plug 1 and the jack 20 by fittingthe male contacts 24 into the corresponding six female contacts 5 on theplug 1 side. The male contacts 24 are electrically connected to a wiringpattern on a wiring panel 22 via a plurality of electrical wirings (notshown), whereby the male contacts 24 are electrically connected to asignal receiving circuit or a signal sending circuit via the wiringpattern.

Push levers 25 and 26 adapted to be fitted into the apertures 17 and 18on the plug 1 side are provided at upper and lower parts of the housing21 and rectangular recesses 27 adapted to receive the projections 19 onthe housing 2 of the plug 1 are formed on the inner wall of the housing21 of the jack 20.

Thus, the projections 19 on the plug 1 and the recesses 27 in the jack20 serve as a guiding member, respectively, when the jack 20 is fittedinto the plug 1 to constitute the optical connector assembly of thepresent invention. In addition, the apertures 17 and the push levers 25serve as a locking member, respectively.

In this manner, with the optical connector assembly as shown in FIGS. 10to 16, the optical fiber fitting unit 30 is threadably connected to theplug 1, while the elastic seal 32 is tightly encased in the jointportion therebetween. Thus, the optical connector assembly of thepresent invention can satisfactorily be used in a severe environmentunder undesirable conditions of vibration, noisy sound, moisture anddust with improved sealability.

FIG. 17 is a sectional view which illustrates an optical connectorassembly in accordance with a second embodiment of the presentinvention. To improve sealability between the plug 1 and the jack 20 aswell as between the jack 20 and the side wall 23 of a box-shaped casing,an O-ring 40 is interposed between the plug 1 and the jack 20 in anassembled state. Additionally, a packing 41 is interposed between thejack 20 and the side wall 23 of the box-shaped casing. In this case, aplurality of male contacts 42 are arranged on the plug 1 side, while aplurality of female contacts 43 are arranged on the jack 20 side. Tothis end, a plurality of holes are formed on the packing 41 so as toallow the female contacts 43 to extend through the packing 41.

To carry out the first and second embodiments of the present invention,the foremost end surface of the optical fiber 9 is treated by using ajig as shown in FIGS. 18 and 19, before the optical fiber 9 is coupledto the plug 1.

As shown in FIGS. 18 and 19, the jig for treating the foremost end faceof the optical fiber 9 comprises a first jig 47 and a second jig 49. Thefirst jig 47 is formed with a threaded hole 45 at the upper end part anda guide hole 46 at the lower end part thereof. The guide hole 46 iscommunicated with the threaded hole 45 in alignment with the latter andhas an inner diameter which is dimensioned substantially same as anouter diameter of the optical fiber 9. The second jig 49 is formed witha hole 48 which is dimensioned so as to allow only a core 9a of theoptical fiber 9 with a sheath 9b removed therefrom to extend through thehole 48.

When the foremost end surface of the optical fiber is to be treated byusing the aforementioned jig, first, the fore end of the core 9a isexposed to the outside by a distance of 1 to 2 mm by removing a part ofthe sheath 9b. Then, while the foregoing state is maintained, theoptical fiber 9 extends through the bolt 31 and the elastic seal 32, asshown in FIG. 19. Thereafter, the bolt 31 is threadably fitted into thethreaded hole 45 in the first jig 47, whereby the elastic seal 32 istightly received in a space at the lower end part of the threaded hole45 and the fore end of the core 9a is protruded outward of the first jig47 while extending through the guide hole 46. It should be noted that apart of the sheath 9b having the same length as that of the guide hole46 or a length appreciably longer than that of the guide hole 46 isreceived in the guide hole 46 of the first jig 47.

Thereafter, while the core 9a is protruded outwardly by a distance of 1to 2 mm and a part of the sheath 9b is likewise protruded outwardly alittle bit, the first jig 47 is brought in pressure contact with thesecond jig 49.

The hole 48 of the second jig 49 is dimensioned to have an innerdiameter larger than an outer diameter of the core 9a but smaller thanan outer diameter of the sheath 9b. Thus, when the first jig 47 isfirmly mounted on the second jig 49, the sheath 9b is fully received inthe guide hole 46. Consequently, the sheath 9b is protected fromdeformation or damage.

If it is required that the foremost end surface of the core 9a is heatedor ground, the second jig 49 is disconnected from the first jig 47 sothat the foremost end surface of the core 9a protruded outward of thefirst jig 47 is ground by using an abrasive paper. It should be addedthat there is no danger that the sheath 9b swells during a grindingoperation, because the outer diameter side of the sheath 9a is firmlyretained within the guide hole 46.

On completion of the grinding operation, the bolt 31 is removed from thefirst jig 47. Thereafter, the bolt 31 is threadably fitted into thethreaded hole 16 (see FIG. 11) on the jig 1 shown in FIG. 10. Now, theoptical fiber 1 of which foremost end face has been treated is ready tobe coupled to the plug 1.

When the first jig 47 is firmly mounted on the second jig 49 as shown inFIG. 18, a distance L between the elastic seal 32 and the foremost endof the core 9a of the optical fiber 9 is approximately set to a lengthof the guide hole 46.

With the conventional technique, since the foremost end surface of anoptical fiber is treated without use of a specially designed jig for theforegoing purpose, there arises a problem that the distance L fails tobe set uniformly. For example, a gap l appears between the foremost endof the optical fiber 9 and the optical element 4, as shown in FIG. 20.This leads to a problem that an optical coupling efficiency is reduced.

The foregoing embodiments have been described above as to a case wherethe direction of extension of the optical fiber 9 intersect thedirection of connection/disconnection of the optical connector assemblyat a right angle.

Next, description will be made below with reference to FIGS. 21 to 23 asto a case where the direction of extension of the optical fiber 9 is inparallel with the direction of connection/disconnection of the opticalconnector assembly.

FIG. 21 is a sectional view which illustrates the whole structure of theoptical connector assembly after the optical fiber 9 is coupled thereto,FIG. 22 is a sectional view which illustrating structure of an opticalmodule 50 before the optical fiber 9 is coupled to the optical connectorassembly, and FIG. 23 is a perspective view which illustrates theoptical fiber side before the optical fiber is coupled to the opticalconnector assembly.

Referring to FIGS. 21 to 23, a guide hole 52 for an optical fiberfitting unit, an optical fiber guide hole 53, an optical elementreceiving hole 54 and an electrical connector fitting hole 55 aresuccessively formed at the central part of a housing 51 of the opticalmodule 50. A printed-circuit board 7 is firmly placed on the bottom wallof the connector fitting hole 55 and an optical element 4 is immovablymounted on the printed-circuit board 7.

The left-hand end part of the connector fitting hole 55 as seen in thedrawings is machined in the form of a threaded hole so that theright-hand male-threaded end part of an electrical module 57 isthreadably fitted into the threaded hole of the connector fitting hole55. Electrical connection of a terminal pin 58 of the electrical module57 to the printed-circuit board 7 is accomplished by a lead wire 59, asshown in FIG. 21. The electrical module 57 is fitted to a various kindof casing to which the optical connector assembly of the presentinvention is fitted. In addition, a plurality of male threads 58 areformed on the right-hand end part of the housing 51 of the opticalmodule 50.

As shown in FIG. 23, an optical fiber fitting unit for the optical fiber9 comprises a cover 61 and an elastic seal 32, and the optical fiber 9extends through a hole in the cover 61 and a hole in the elastic seal32. The cover 61 is formed with a plurality of female threads 62. Whenthe optical fiber 9 is coupled to the housing 51 side, the femalethreads 62 in the cover 61 are threadably engaged with a plurality ofmale threads 58 on the housing 51 of the optical module 50. Once thecover 61 is threadably fitted to the housing 51 of the optical module50, the foremost end of the optical fiber 9 is brought in close contactwith a light emitting/light receiving surface of the optical element 4,while an elastic seal 32 is tightly encased in the deepest part of theguide hole 52, as shown in FIG. 21.

FIG. 24 is a sectional view which illustrates an optical connectorassembly in accordance with an embodiment of the present inventionmodified from the embodiment which has been described above withreference to FIG. 21. In this modified embodiment, the cover 61 is fullymade of elastomeric material, e.g., hard rubber or the like material.Therefore, the elastic seal 32 in the preceding embodiment of thepresent invention is not required. According to the modified embodimentof the present invention, since the foremost end of the cover 61 made ofelastomeric material is brought in pressure contact the inside wall ofthe housing of the optical module 50, the optical fiber 9 can firmly beheld by the cover 61. It should of course be understood that the cover61 need not be constituted by elastomeric material but only the foremostend of the cover 61 adapted to come in pressure contact with the insidewall of the housing 51 may be made of elastomeric material.

FIG. 25 is a perspective view which schematically illustrates an opticalconnector assembly of the present invention which is used as an opticalsignal sending module. The optical signal sending module 70 having theoptical fiber 9 coupled thereto includes a minus terminal Y leading to adirect current power supply source 71, a plurality of plus terminals X₁to X_(n) leading to the power supply source 71 and a terminal SIG towhich data are fed, whereby the power supply source 71 can selectivelybe connected to the minus terminal Y and one of the plural plusterminals X₁ to X_(n).

FIG. 26 is a wiring diagram which illustrates by way of example astructure of circuits in the optical signal sending module 70.Specifically, the optical signal sending module 70 comprises a lightemitting diode driving circuit board (hereinafter referred to as LEDdriving circuit board) 72 and a connector 73. The LED driving circuitboard 72 includes a LED 74 and a plurality of fixed resistors r₁ tor_(n) connected to the LED 74 in parallel with the latter to properlyadjust an intensity of optical power. On the other hand, the connector 3includes a plurality of plus terminals X₁ to X_(n) leading to a powersupply source (not shown), a terminal Z to which data are fed and aminus terminal Y leading to the power supply source in the same manneras described above with reference to FIG. 25. The plus terminals X₁ toX_(n) are connected directly to the fixed resistors r₁ to r_(n) in theLED driving circuit board 72 via a plurality of conductors or aplurality of art work wirings 75 on the LED driving circuit board 72 inan one-to-one relationship.

When the optical signal sending module 70 is connected to a power supplysource (not shown) in field, it is required that a corresponding tablerepresenting, e.g, a relationship between a length of the optical fiber(i.e. a distance of signal transmission) and the plural terminals X₁ toX_(n) is previously produced. Thus, an operator can select an optimumintensity of light emitting power for the LED 74 merely by connecting asuitable terminal (one of the terminals X₁ to X_(n)) in the opticalsending module 70 to the power supply source with reference to thecorresponding table. Consequently, he can easily perform an adjustingoperation in field.

FIG. 27 is a wiring diagram for the optical signal sending module 70 inaccordance with an embodiment of the present invention modified from theembodiment which has been described above with reference to FIG. 26. Inthis modified embodiment, a plurality of fixed resistors r₁ ' to r_(n) 'are connected to each other in series so as to adjust an intensity oflight emitting power.

With the optical signal sending module 70 as constructed in theabove-described manner, a value of resistance of each of the pluralresistors r₁ ', r₂ ', - - - r_(n) ' is determined as follows.

Namely, when a composite resistor for each of the plural resistors r₁ ',r₂ ', - - - r_(n) ' required in correspondence to variation of adistance of signal transmission (i.e., a length of the optical fiber) isrepresented by R₁, R₂, - - - R_(n), a value of resistance of each of theresistors r₁ ', r₂ ', - - - r_(n) ' is preset such that the followingequations are established for the respective composite resistor R₁,R₂, - - - R_(n). ##EQU1## In other words, when a value of resistance ofthe plural resistors connected in parallel with each other as shown inFIG. 26 is represented by r₁, r₂, - - - r_(n), a value of resistance ofeach of the resistors r₁ ', r₂ ' - - - r_(n) ' is set such thatequations of r₁ =R₁, r₂ =R₂, - - - r_(n) =R_(n) are established.

With such construction derived from the serial connection, even in acase where the power supply source 71 is incorrectly connected to two ormore terminals among the plural terminals X₁ to X_(n), it is assuredthat no electric current is fed to the LED 74 with a rating in excess ofthe maximum rated value.

For example, in a case where the power supply source 71 having a voltageV is incorrectly connected to the plus terminals X₁ and X₂, an electriccurrent I to be fed to the LED 74 is represented by the followingequations. ##EQU2## This case is substantially equivalent to a casewhere the power supply source is connected only to the plus terminal X₂.

Similarly, also in a case where the power supply source 71 isincorrectly connected to three or more plus terminals, the remainingresistors ranging from the resistor located nearest to the LED 74 amongthe plural resistors r₁ ' to r_(n) ' till the LED 74 have a significanteffect on the electric current I but other resistors have no effect onthe electric current I.

Therefore, if R_(n) is set such that an equation of I=V/R_(n) satisfiesa condition of the maximum rated electric current, there is no dangerthat the LED 74 is undesirably damaged or injured by an excessively highintensity of electric current irrespective of how far incorrectconnection is made.

FIG. 28 is a wiring diagram which illustrates an optical signalreceiving circuit for discriminating the logical level of an opticalsignal received via the optical fiber, after the received optical signalis converted into an electrical signal. A signal derived fromintegration of received optical signals is inputted into a firstcomparator 80. In this case, illustration of a structure of anintegration circuit for adding the signal derived from integration to aninverted input terminal (minus terminal) of the first comparator 80 aswell as a positive feedback circuit for adding an output from the firstcomparator 80 to a non-inverted input terminal (plus terminal) iseliminated for the purpose of simplification.

In FIG. 28, reference numeral 80 designates a first comparator in whicha signal derived from integration of received optical signals isinputted into the inverted input terminal (minus terminal) and apositive feedback signal derived from the positive feedback circuit isinputted into the non-inverted input terminal (plus terminal) so that asignal level of the former signal is compared with a signal level of thelatter signal, reference numeral 82 designates a voltage dividingcircuit for dividing a voltage V_(cc) of the power supply source byresistors R₁ and R₂ and reference numeral 81 designates a secondcomparator in which an output derived from comparison made in the firstcomparator 80 is inputted into the inverted input terminal and a voltagedivided by the voltage dividing circuit 82 is inputted into thenon-inverted terminal. A signal representative of an output derived fromcomparison made in the second comparator 81 is fed to a data processingcircuit which is not shown in the drawing. The first and secondcomparators 80 and 81 are activated with a constant voltage V_(cc) ofthe power supply source.

With the circuits shown in FIG. 28, the voltage V_(cc) to be applied toan output terminal of the first comparator 80 is restricted by a Zenerdiode 83 within a predetermined voltage range so that the secondcomparator 81 is operated normally.

To assure that the second comparator 81 is operated normally, it isrequired that a voltage value of the signal to be inputted into theinverted input terminal is reduced lower than a predetermined voltagevalue (i.e., the upper limit value of a voltage for normally operatingthe second comparator 81). This upper limit value V_(in) is definitelydetermined by the voltage value V_(cc) of the power supply source andvaries depending on characteristics of the second comparator 81. Ingeneral, the upper limit value V_(in) is approximately set to 80% of thevoltage value V_(cc).

Therefore, it is required that the maximum voltage value appearing at anoutput terminal A of the first comparator 80 is set lower than the upperlimit value V_(in) for normally operating the second comparator 81.

To meet the requirement with the above-described construction, thevoltage V_(cc) of the power supply source (collector voltage) is fed tothe output terminal A via resistors R₃ and R₄. In addition, the Zenerdiode 83 is connected to the intermediate location between the bothresistors R₃ and R₄ (so that an inverse voltage is applied to the Zenerdiode 83).

In this case, a Zener voltage V_(z) of the Zener diode 83 is previouslyselected such that the following inequality is established.

    V.sub.z ≦V.sub.in <V.sub.cc                         (1)

In a case where the maximum voltage value appears at the output terminalA, i.e., in a case where an output derived from comparison made in thefirst comparator 80 reaches a logic "1" level, the voltage value at theoutput terminal A becomes a Zener voltage value V_(z) for the Zenerdiode 83.

Thus, it is assured that the second comparator 81 is normally operated,even when the above inequality (1) is established and the voltage valueV_(z) is inputted into the inverted input terminal of the secondcomparator 81.

Alternatively, a circuit structure as shown in FIG. 29 wherein a Zenerdiode 83 is likewise used may be substituted for the circuit in FIG. 28with the same advantageous effects.

Specifically, with the structure shown in FIG. 29, the voltage V_(cc) ofthe power supply source is connected to an output terminal B of thefirst comparator 80 via a resistor R₅ and the Zener diode 83 isconnected to an input terminal C of the second comparator 81 (so that aninverse voltage is applied to the input terminal C of the secondcomparator 81). In addition, a resistor R₆ is connected to theintermediate location between the both terminals B and C.

Also in this case, the maximum value of a voltage appearing at theoutput terminal B becomes equal to a Zener voltage V_(z) of the Zenerdiode 83, whereby the inequality (1) is established. Consequently, it isassured that the second comparator 81 is normally operated.

It should be noted that the present invention may be carried out withthe resistor R₆ in FIG. 29 removed from the circuit system.

Next, description will be made below as to another modified embodimentof the present invention wherein a circuit structure is embodied withthe same advantageous effects as those derived from the embodiments asin FIGS. 28 and 29 in such a manner that merely a plurality of resistorsare used but no Zener diode is used.

In detail, as shown in FIG. 30, according to the modified embodiment ofthe present invention, a voltage V_(cc) of the power supply source(collector voltage) is fed to an output terminal D of the firstcomparator 80 via a resistor R₇. One end of a resistor R₈ is connectedto the output terminal D and the other end of the resistor R₈ isearthed, whereby a voltage dividing circuit for dividing the voltageV_(cc) of the power supply source is constructed by using the resistorsR₇ and R₈.

In this case, to assure that the second comparator 81 is normallyoperated, it is required that the maximum voltage value at the outputterminal D, i.e., the divided voltage V_(out) is reduced lower than theupper limit value V_(in) of a voltage for normally operating the secondcomparator 81 (refer to the following inequality (2)).

    V.sub.out ≦V.sub.in <V.sub.cc                       (2)

As will be apparent from the drawing, the divided voltage V_(out) can berepresented by the following equation.

    V.sub.out ={R.sub.8 /(R.sub.7 +R.sub.8)}·V.sub.cc (3)

Thus, the second comparator 81 can normally be operated by properlyselecting the resistors R₇ and R₈ so as to satisfy the inequality (2)and the equation (3).

Additionally, the present invention may be embodied as shown in FIG. 31.According to the embodiment of the present invention in FIG. 31, avoltage V_(cc) of the power supply source is fed to an output terminal Eof the first comparator 80 via a resistor R₉, and one end of a resistorR₁₁ is connected to an input terminal F of the second comparator 81,while the other end of the resistor R₁₁ is earthed. In addition, aresistor R₁₀ is connected to the intermediate location between the bothterminals E and F. In a case where the voltage V_(cc) of the powersupply source is divided by using the resistors R₉, R₁₀ and R₁₁, thedivided voltage value at the input terminal F is represented by thefollowing equation.

    V.sub.out ={R.sub.11 /(R.sub.9 +R.sub.10 +R.sub.11)}·V.sub.cc(4)

Thus, normal operation of the second comparator 81 can be achieved byproperly selecting the resistors R₉, R₁₀ and R₁₁ so as to satisfy theabove equation.

According to the aforementioned embodiments of the present invention, avoltage divided so as to allow the voltage V_(cc) of the power supplysource to be reduced lower than the voltage V_(in) for normallyoperating the second comparator 81 by using a Zener diode or a pluralityof resistors is applied to the output terminal of the first comparator80, whereby a voltage to be inputted into the input terminal of thesecond comparator 81 is properly adjusted within the correct operativerange. Alternatively, the present invention may be embodied with thesame advantageous effects as those derived from the foregoingembodiments by boosting the voltage V_(cc) of the power supply source tobe fed to the second comparator 81 thereby to raise up the upper limitvoltage of the correct operative range.

Specifically, as shown in FIG. 32, a boosting circuit 85 (of the typee.g., including an AC/DC converter as an essential component) isarranged between the second comparator 81 and the voltage V_(cc) of thepower supply source so that the voltage V_(cc) of the power supplysource is boosted to a predetermined value of voltage V_(up) by theboosting circuit 85. Then, the thus boosted voltage V_(up) is fed to thesecond comparator 81.

The upper limit value V_(in) ' of voltage for normally operating thesecond comparator 81 is definitely determined by the boosted voltageV_(up).

When the maximum value of a voltage appearing at an output terminal G ofthe first comparator 80 is represented by V_(cc) (held at a logical "1"level) as shown in the drawing, a condition for normally operating thesecond comparator 81 is expressed by the following inequality.

    V.sub.cc ≦V.sub.in '                                (5)

Thus, the second comparator 81 can normally be operated by boosting thevoltage V_(cc) of the power supply source to a boosted voltage V_(up) soas to establish the above inequality (5).

With the conventional circuit structure shown in FIG. 8, there arises aproblem that a normal output wave form can not be obtained in the firstcomparator 81, as shown in FIGS. 9(a) and (b). In contrast with theconventional circuit structure, according to the embodiment of thepresent invention, an essentially ideal wave form as shown in FIG. 9(c)can be obtained by employing the circuit structure as described above.

INDUSTRIAL APPLICABILITY

The optical connector assembly of the present invention isadvantageously employable for the purpose of making opticalcommunication under a normal control for various kinds of industrialapparatuses or equipments to be operated in a severe environmentincluding vibration, noisy sound, contaminated material, moisture ordust, e.g., facilities in a factory or industrial machinery.

We claim:
 1. A comparator circuit including a first comparator formaking comparison as to a level of an input signal, a second comparatorfor allowing an output derived from said comparison made by said firstcomparator to be inputted into one input terminal of said secondcomparator so as to make comparison with a predetermined referencesignal as to a level of said reference signal, and a power supply sourcehaving a predetermined magnitude of voltage for activating said firstand second comparators, said power supply source being electricallyconnected to an output terminal of the first comparator so as to allowthe maximum value of an output derived from the comparison made by thefirst comparator to be equalized to said predetermined magnitude ofvoltage, whereinsaid comparator circuit further includes a voltagedividing circuit for dividing a voltage of the power supply source to beapplied to said output terminal of the first comparator such that themaximum value of voltage inputted into said one input terminal of thesecond comparator is equalized to a voltage of which magnitude is setwithin the range for normally operating the second comparator, a voltagederived from said dividing being applied to said output terminal of thefirst comparator.
 2. A comparator circuit including a first comparatorfor making comparison as to a level of an input signal, a secondcomparator for allowing an output derived from said comparison made bysaid first comparator to be inputted into one input terminal of saidsecond comparator so as to make comparison with a predeterminedreference signal as to a level of said reference signal, and a powersupply source having a predetermined magnitude of voltage for activatingsaid first and second comparators, said power supply source beingelectrically connected to an output terminal of the first comparator soas to allow the maximum value of an output derived from said comparisonmade by the first comparator to be equalized to said predeterminedmagnitude of voltage, whereinsaid comparator circuit further includes aboosting circuit for boosting a voltage of the power supply source to beapplied to the second comparator, said boosting circuit being interposedbetween the second comparator and the power supply source, whereby avoltage derived from said boosting in the boosting circuit allows thesecond comparator to be normally operated when said predeterminedmagnitude of voltage is inputted into said one input terminal of thesecond comparator.